1. Technical Field
The present invention relates to an image forming apparatus such as an electrophotographic copier, a printer, a facsimile machine or the like and an image density correction device used therein.
2. Related Art
As a conventional image forming apparatus, an apparatus having plural submodules such as an photoconductor drum, a charging device, an exposure device, developing device and a transfer device is known. In such image forming apparatus, the rotating photoconductor drum is uniformly charged with the charging device. Next, the surface of the charged photoconductor drum is selectively exposed with the exposure device, thereby an electrostatic latent image is formed on the photoconductor drum. Then the electrostatic latent image formed on the photoconductor drum is developed with the developing device thereby visualized, and an obtained toner image is transferred onto a recording material.
In such image forming apparatus, to suppress density variation of a printed image, a toner image in a predetermined pattern is formed at predetermined timing, and based on the result of detection of the density of the formed toner image, operation parameters of the respective submodules of the image forming apparatus are adjusted. As the operation parameters, a charging bias in the charging device, the quantity of light emitted from the exposure device, a developing bias and a toner supply amount in the developing device, the output of the transfer device and the like can be given.
In the image forming apparatus, a predetermined error is allowed in the photoconductor drum and a photoconductive layer formed on the photoconductor drum. Accordingly, even when the above-described operation parameters are appropriately set, non-uniformity in density may occur in a rotation direction of the photoconductor drum i.e. a slow-scanning direction. Further, in addition to the photoconductor drum, respectively predetermined dimensional errors are allowed in a charging roller provided in the charging device, a developing roller provided in the developing device, a transfer roller provided in the transfer device and the like. Accordingly, these submodules may cause non-uniformity in density in the slow-scanning direction upon image formation.